1. Field of the Invention
The present invention generally relates to a filter, and more particularly to a band pass filter.
2. Related Art
A filter is able to eliminate interference signals in a communication product. Features of an ideal filter are that signal attenuation is zero within a pass band and becomes infinite within a cut-off band, and a fluctuation from the pass band to the cut-off band should be as sharp as possible. Nowadays, people produce a filter by placing different resonators in different forms. Filters made of step resonators are called low band pass filters. When the low band pass filter is used in a wireless fidelity (WIFI) phone of 2.45 GHz, the low band pass filter cannot effectively eliminate noise caused by nearby global system for mobile communication (GSM) mobile phones working at 1.9 GHz.
Therefore, a heretofore unaddressed need exists in the industry to overcome the aforementioned deficiencies and inadequacies.